The attack on Combat Outpost Sayed Abad killed five Afghans, including a security guard and an interpreter, and also wounded 17 Afghans.

Lt. Col. Wayne Perry, a spokesman for the NATO-led International Security Assistance Force (ISAF), told NBC News that none of the 77 hurt Americans appeared to have suffered life-threatening injuries.

"The majority of injured ISAF personnel will likely return to duties shortly," an ISAF statement added.

The suicide bomber was driving a truck carrying firewood when he rammed into the outpost's entrance, according to NATO.

"Most of the force of the explosion was absorbed by the protective barrier," ISAF said in a statement.

Quoting US Army spokesman Major David Eastburn, AFP reported that the explosion left a "20-foot hole in the wall."

However, ISAF said Sunday that the outpost "remains operational and protective barriers have been repaired."

The explosion broke windows in government offices nearby, said Roshana Wardak, a former parliamentarian who runs a clinic in the nearby town of the same name.

'American colonialism'

The Taliban claimed responsibility for the attack, which came hours after the movement vowed to keep fighting U.S. forces in Afghanistan until all American troops leave the country. The Taliban said that their movement had nothing to do with the Sept. 11 attacks.

"Each year, 9/11 reminds the Afghans of an event in which they had no role whatsoever," a Taliban statement emailed to media said. "American colonialism has shed the blood of tens of thousands of miserable and innocent Afghans."

The United States and its allies invaded Afghanistan on Oct. 7, 2001, after the Taliban, who then ruled the country, refused to hand over Osama bin Laden.

The late al-Qaida leader was at the time living in Afghanistan, where the terror network had training camps from which it planned attacks against the U.S. and other countries.

"The Afghans have an endless stamina for a long war," the statement said. "Through a countrywide uprising, the Afghans will send the Americans to the dustbin of history like they sent other empires of the past."

The statement was issued by the Islamic Emirate of Afghanistan, the official title used by the Taliban when they ruled the country.

The attack occurred just 43 miles from Kabul in an increasingly lawless district that is just an hour's drive from the capital and is in a key province that controls a strategic approach to Kabul.

Sayed Abad is seven miles east of the Tangi Valley, where the Taliban on Aug. 6 shot down a U.S. military helicopter, killing 30 Americans. Many of the dead belonged to the U.S. Navy's SEAL Team 6 — the same elite unit that killed bin Laden during a May 2 cross-border raid into Pakistan, where al-Qaida's leadership was driven. It was the deadliest single loss for American forces in the decade-old war.

"Some back home have asked why we are still here," U.S. Ambassador Ryan Crocker said at a 9/11 memorial at the embassy in Kabul. "It's been a long fight and people are tired. The reason is simple. Al-Qaida is not here in Afghanistan, and that is because we are. "

"We're here so that there is never again another 9/11 coming from Afghan soil. We, with our Afghan partners, figured out that the best way to ensure that is to work together and with the international community for a stable, secure, democratic Afghanistan."

Marine Corps Gen. John Allen, the commander of U.S. and NATO troops in Afghanistan urged those assembled to honor the memory of those who died.

"On that day we lost mothers and fathers, sons and daughters we lost people of many nations and many religions, today we remember, we honor them all," he said.

In addition to the attack in Wardak on Saturday, 10 Afghan civilians were killed in two separate roadside bombings.

While the overall international death toll dropped by 14 percent in the first half of the year, the number of Americans who died remained virtually unchanged, 197 this year compared with 195 in the first six months of last year, according to a tally by The Associated Press.

In a midyear report last July, the U.N. said 1,462 Afghan civilians also lost their lives in the first six months of this year in the crossfire of the battle between Taliban insurgents and Afghan, U.S. and NATO forces. During the first half of last year, 1,271 Afghan civilians were killed.